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Lesson 1
🌱 What is a living thing?
Hello! Biology is the science of living things. Its name comes from the Greek words "bios" (life) and "logos" (knowledge). Anyone who studies animals, plants, fungi or tiny living things we can't see is a biologist.
How can we tell if something is alive? Living things feed, respire (release energy from food), grow and reproduce — they make young that look like them. A rock does none of these things.
Living things respond to changes around them: a sunflower turns to the sun, a cat pricks up its ears at a sound. They also get rid of waste made in their bodies — this is called excretion. Most animals can also move from place to place.
And most important of all: every living thing is made of cells. Some, like bacteria, are just a single cell. An elephant is made of trillions of them. So: nutrition, respiration, growth, reproduction, response, excretion and movement — the 7 signs of life!
Key words
- Biology
- The science of living things.
- Excretion
- Getting rid of waste made inside the body.
- Reproduction
- Making young that are like the parent.
💡 Did you know? Koala: It can sleep 18 to 22 hours a day, because its leaves give very little energy. Meet the animal →
Quick quiz
Which of these is NOT a feature of living things?
A) Feeding · B) Growing · C) Rusting · D) Reproducing
Answer
C) Rusting: Rusting happens to non-living things like iron; it is not a sign of life.
A sunflower turning towards the sun is an example of…
A) Response · B) Excretion · C) Reproduction · D) Respiration
Answer
A) Response: The sunflower responds to a change around it: the light.
What are all living things made of?
A) Stones · B) Cells · C) Bones · D) Leaves
Answer
B) Cells: From single-celled bacteria to giant elephants, all living things are made of cells.
Lesson 2
🦠 Cells: the building blocks of life
A house is built from bricks; living things are built from cells. Cells are so small that we can see most of them only with a microscope. Robert Hooke named them "cells" in 1665, after seeing tiny rooms when he looked at cork through a microscope.
An animal cell has three main parts. The cell membrane wraps the cell like a bag and controls what goes in and out. The jelly-like liquid that fills it is the cytoplasm. The nucleus is the control centre, where DNA — the instructions — is kept.
Plant cells have two extra parts. The cell wall sits outside the membrane like a strong box and helps the plant stand upright. Chloroplasts are tiny factories that give leaves their green colour and make food from sunlight.
Cells multiply by dividing: one cell becomes two, two become four. That is how we grow and how a cut on your knee heals. Bacteria are single-celled living things with no nucleus; their DNA floats in the cytoplasm.
Key words
- Cell membrane
- The thin layer around a cell that controls what goes in and out.
- Nucleus
- The control centre of the cell, where DNA is kept.
- Chloroplast
- The green part of a plant cell that makes food from sunlight.
💡 Did you know? Giant panda: A newborn panda cub weighs about as much as a stick of butter. This tiny cub turns into a big panda as its cells divide and multiply. Meet the animal →
Quick quiz
Which part is the control centre of the cell?
A) Cell membrane · B) Cytoplasm · C) Nucleus · D) Cell wall
Answer
C) Nucleus: The nucleus keeps the DNA and runs the cell.
Which of these is found only in plant cells?
A) Chloroplast · B) Nucleus · C) Cell membrane · D) Cytoplasm
Answer
A) Chloroplast: Chloroplasts let plants make food from sunlight; animal cells don't have them.
How does a cut on your knee heal?
A) Cells divide and multiply · B) Bones get longer · C) Blood turns to stone · D) Skin gets painted
Answer
A) Cells divide and multiply: Cells around the cut divide and the new cells fill the gap.
Lesson 3
🗂️ Sorting living things
There are millions of kinds of living things on Earth! To make sense of them, scientists sort them into groups by how alike they are. This is called classification — think of books being arranged on library shelves.
The biggest groups are animals, plants, fungi, and microscopic living things such as bacteria. Fungi are not plants! They can't make their own food; they absorb it from their surroundings.
Animals are first split in two. Those with a backbone are vertebrates; those without are invertebrates. Insects, spiders, worms, snails and octopuses are invertebrates — and they make up the vast majority of animal species!
Vertebrates come in 5 groups. Mammals feed their young on milk, and most are hairy. Birds have feathers and beaks. Reptiles have scaly skin. Amphibians start life in water and can live on land too. Fish breathe in water through their gills.
Key words
- Vertebrate
- An animal with a backbone.
- Mammal
- A vertebrate that feeds its young on milk.
- Species
- A group of similar living things that can breed together.
💡 Did you know? Red kangaroo: Its baby is born as small as a jelly bean and grows up in its mother's pouch. Kangaroos are mammals: the joey drinks milk inside its mother's pouch. Meet the animal →
Quick quiz
Which group does the octopus belong to?
A) Fish · B) Invertebrates · C) Reptiles · D) Mammals
Answer
B) Invertebrates: An octopus has no backbone — no bones at all — so it is an invertebrate.
What do we call animals that feed their young on milk?
A) Birds · B) Amphibians · C) Mammals · D) Reptiles
Answer
C) Mammals: Feeding young on milk is the key feature of mammals — dolphins and whales are mammals too.
Which is true about fungi?
A) They are a kind of plant · B) They make food from sunlight · C) They are a group of their own · D) They are vertebrates
Answer
C) They are a group of their own: Fungi are neither plants nor animals: they are a separate group that absorbs food from around them.
Lesson 4
☀️ Plants and photosynthesis
When we're hungry, we eat. Plants make their own food instead! This is called photosynthesis, which means "putting together with light".
A plant needs three things: sunlight, water and carbon dioxide gas from the air. The roots take water from the soil, tiny pores in the leaves take in carbon dioxide, and green chlorophyll captures the sun's energy.
From these, the plant makes sugar, which it uses to grow. And it leaves a gift: oxygen! The oxygen we breathe comes from plants and from tiny algae in the oceans, which make about half of it.
Photosynthesis is where almost all life on Earth begins. Herbivores eat plants, and carnivores eat herbivores. So even a lion's energy really comes from the sun!
Key words
- Photosynthesis
- Plants making food and oxygen from light, water and carbon dioxide.
- Chlorophyll
- The green substance in plants that captures light.
- Carbon dioxide
- A gas in the air that plants use to make food.
💡 Did you know? African elephant: An elephant can eat more than 150 kilograms of plants a day. All those plants were grown by sunlight and photosynthesis. Meet the animal →
Quick quiz
Which gas does a plant give off during photosynthesis?
A) Carbon dioxide · B) Oxygen · C) Smoke · D) Steam
Answer
B) Oxygen: Plants take in carbon dioxide and give off oxygen — the oxygen we breathe.
What makes a leaf green?
A) Chlorophyll · B) Water · C) Soil · D) Sugar
Answer
A) Chlorophyll: Chlorophyll captures sunlight and makes leaves look green.
Where does a plant mostly take in water?
A) Its leaves · B) Its flowers · C) Its roots · D) Its bark
Answer
C) Its roots: Roots soak up water from the soil and it travels up the stem to the leaves.
Lesson 5
🔗 Food chains
On the steppe, a ground squirrel eats grass, and an eagle catches the squirrel. This "who eats whom" line is called a food chain. The arrows show which way the energy goes.
A chain always starts with a producer: a plant that makes its own food. Animals that eat plants are herbivores; those that eat other animals are carnivores. Animals like the brown bear that eat both are omnivores.
The hidden heroes are the decomposers. Fungi and bacteria break down dead plants and animals, returning their nutrients to the soil so new plants can grow. In nature, nothing goes to waste!
In real life, chains link up to form a food web. At each step most of the energy is used up and only about a tenth passes on. That's why there are far fewer eagles than ground squirrels in nature.
Key words
- Producer
- A living thing that makes its own food (plants, algae).
- Consumer
- A living thing that gets food by eating other living things.
- Decomposer
- Fungi and bacteria that break down dead things into the soil.
💡 Did you know? Anatolian ground squirrel: It is important food for eagles, hawks and foxes — a key animal of the steppe. Meet the animal →
Quick quiz
What does a food chain always start with?
A) A carnivore · B) A producer · C) A decomposer · D) An omnivore
Answer
B) A producer: Every chain starts with a producer — a plant that turns sunlight into food.
The brown bear eats plants and meat. It is a(n)…
A) Herbivore · B) Carnivore · C) Omnivore · D) Producer
Answer
C) Omnivore: Animals that eat both plants and animals are omnivores.
What breaks dead leaves down into the soil?
A) Fungi and bacteria · B) Eagles · C) Stones · D) The wind
Answer
A) Fungi and bacteria: Fungi and bacteria are decomposers; they return nutrients to the soil.
Lesson 6
🫁 How living things breathe
Our bodies need oxygen to use the energy in food. Cells "burn" food with oxygen to release energy, leaving carbon dioxide behind. This is respiration. By breathing in and out, we take in oxygen and get rid of carbon dioxide.
Mammals, birds and reptiles breathe with lungs. Dolphins and whales are mammals too: even though they live in water, they have lungs, and they surface to breathe through the blowhole on top of their head.
Fish use the oxygen dissolved in water. Water goes in through the mouth and flows over the gills, where oxygen passes into the blood. That's why a fish can't breathe out of water.
Frogs breathe with their lungs and also through their thin, damp skin. Insects have tiny tubes called tracheae that run in from small holes in their body, carrying air straight to their cells. Plants respire too!
Key words
- Respiration
- Cells releasing energy from food using oxygen.
- Gills
- The organs fish use to take oxygen from water.
- Lungs
- The organs that pass oxygen from the air into the blood.
💡 Did you know? Bottlenose dolphin: When it sleeps, only half its brain rests; the other half keeps it breathing. Meet the animal →
Quick quiz
Which organ do fish breathe with?
A) Lungs · B) Gills · C) Tracheae · D) A trunk
Answer
B) Gills: Gills pass the oxygen in water into the blood.
What does a dolphin do to breathe?
A) Opens its gills · B) Comes up to the surface · C) Dives to the sea floor · D) It never breathes
Answer
B) Comes up to the surface: A dolphin is a mammal with lungs; it breathes through the blowhole on its head.
Which gas is made in cells during respiration and breathed out?
A) Oxygen · B) Carbon dioxide · C) Helium · D) Nitrogen
Answer
B) Carbon dioxide: Cells use oxygen and make carbon dioxide, which we breathe out.
Lesson 7
❤️ The heart and blood
Your heart is a very strong muscle about the size of your fist. It squeezes and relaxes non-stop, pumping blood all round your body. You can feel each beat as your pulse in your wrist. At rest, a heart beats roughly 60 to 100 times a minute — a little faster in children.
Blood travels through tubes called blood vessels. Arteries carry blood away from the heart; veins bring it back. Between them are capillaries, thinner than a hair, which reach right up to the cells.
Blood is like a delivery truck: it takes oxygen from the lungs and food from the intestines to the cells, and picks up carbon dioxide and waste on the way back. Red blood cells carry oxygen, white blood cells fight germs, and platelets help stop bleeding when you get a cut.
A human heart has four chambers. Animal hearts can be different: a fish's heart has two chambers, and an octopus has three hearts and blue blood!
Key words
- Artery
- A blood vessel that carries blood away from the heart.
- Vein
- A blood vessel that brings blood back to the heart.
- Pulse
- The beat you can feel in your blood vessels each time the heart pumps.
💡 Did you know? Blue whale: Its heart weighs about 180 kilograms. Meet the animal →
Quick quiz
What is the heart's job?
A) Digesting food · B) Pumping blood round the body · C) Making oxygen · D) Moving bones
Answer
B) Pumping blood round the body: The heart squeezes like a pump to send blood all round the body.
Which cells carry oxygen in the blood?
A) Red blood cells · B) White blood cells · C) Nerve cells · D) Bone cells
Answer
A) Red blood cells: Red blood cells pick up oxygen in the lungs and carry it to the cells.
What are the vessels that carry blood away from the heart called?
A) Veins · B) Arteries · C) Gills · D) Nerves
Answer
B) Arteries: Arteries carry blood away from the heart; veins bring it back.
Lesson 8
🍽️ Digestion: the journey of food
Before our bodies can use food, it has to be broken down into very tiny pieces — this is digestion. It starts in the mouth: teeth chew the food, and saliva softens it and starts breaking it down.
When you swallow, the food slides down the food pipe (oesophagus) to the stomach. The stomach churns it with strong muscles and mixes it with stomach juices into a mush.
The main work happens in the small intestine, where food is broken into its smallest pieces and passes through the intestine wall into the blood. It's folded up to fit in your tummy, but stretched out it would be several metres long. The large intestine takes back water, and what's left leaves the body as waste.
Animals digest food in many ways. Cud-chewing animals like cows have a stomach with four parts — they bring swallowed grass back up and chew it again. Birds have no teeth; a muscular part of the stomach called the gizzard grinds their food.
Key words
- Digestion
- Breaking food down into tiny pieces the body can use.
- Small intestine
- The long, folded tube where food passes into the blood.
- Gizzard
- The muscular part of a bird's stomach that grinds food.
💡 Did you know? Nile crocodile: It swallows stones that help grind up food and keep it balanced in the water. Meet the animal →
Quick quiz
Where does digestion begin?
A) In the stomach · B) In the mouth · C) In the large intestine · D) In the heart
Answer
B) In the mouth: Teeth chew and saliva softens the food — digestion begins in the mouth.
Where does most food pass into the blood?
A) The small intestine · B) The food pipe · C) The mouth · D) The lungs
Answer
A) The small intestine: Food is broken into its smallest pieces in the small intestine and passes into the blood there.
How do birds, which have no teeth, grind their food?
A) By chewing with their beak · B) With a stomach part called the gizzard · C) With their claws · D) They don't
Answer
B) With a stomach part called the gizzard: A bird's muscular gizzard grinds its food.
Lesson 9
🦴 Skeletons and movement
The skeleton is the body's frame: it gives shape, holds us upright and protects organs like the brain and heart. The skull guards the brain, and the ribs wrap around the heart and lungs like a shield.
Bones can't move on their own. Muscles attached to them contract, get shorter and pull the bone. Places where bones meet are called joints — your elbow and knee are joints. An adult human skeleton has 206 bones.
Insects and crabs wear their skeleton on the outside — an exoskeleton. It protects them like armour but can't grow, so as they get bigger they climb out of the old one and form a new one.
An octopus has no bones at all, so it can squeeze through tiny gaps. Birds have light bones with hollow spaces inside, which helps them fly. Every animal's skeleton suits the way it lives.
Key words
- Joint
- A place where two bones meet and move.
- Backbone (spine)
- The chain of bones called vertebrae along the back.
- Exoskeleton
- The hard outer shell of insects and crabs.
💡 Did you know? Giraffe: A giraffe's neck has only 7 bones, the same as ours — each one is just very long. Meet the animal →
Quick quiz
What moves our bones?
A) Muscles · B) Hair · C) Nails · D) Blood
Answer
A) Muscles: Muscles contract and get shorter, pulling the bones.
What is an insect's skeleton called?
A) Endoskeleton · B) Exoskeleton · C) Spine · D) Skull
Answer
B) Exoskeleton: An insect's hard shell is on the outside: an exoskeleton.
How many bones does an adult human have?
A) 26 · B) 106 · C) 206 · D) 2006
Answer
C) 206: Adults have 206 bones; babies have more, and some fuse together as they grow.
Lesson 10
👂 Senses: picking up the world
We have five senses: sight, hearing, smell, taste and touch. Eyes, ears, nose, tongue and skin collect information about the world. Nerves carry it to the brain as electrical signals, and the brain works out what it means.
Some animals have senses far stronger than ours. Eagles spot prey from very far away. Dogs and wolves smell scents we could never notice.
Dolphins and bats "see" with sound. They make clicks and listen for the echoes bouncing back, which tell them where things are and how big they are — even in the dark. This is called echolocation.
Some animals have senses we don't have at all. Sharks feel tiny electric signals in the water, and some snakes can sense the body heat of their prey in the dark. Each animal's senses suit where it lives and how it finds food.
Key words
- Nerve
- A pathway that carries messages between the senses and the brain.
- Echolocation
- Finding things by listening to echoes.
💡 Did you know? Great white shark: It can sense tiny electric signals in the water. Meet the animal →
Quick quiz
What do we call it when dolphins sense their surroundings with sound?
A) Photosynthesis · B) Echolocation · C) Camouflage · D) Migration
Answer
B) Echolocation: A dolphin makes sounds and listens to the echoes to sense what's around it.
What carries information from the senses to the brain?
A) Muscles · B) Nerves · C) Bones · D) Veins
Answer
B) Nerves: Nerves send the information to the brain as electrical signals.
Which is NOT one of our five senses?
A) Taste · B) Hearing · C) Sensing electricity · D) Touch
Answer
C) Sensing electricity: Sharks can sense electricity; humans can't.
Lesson 11
🐸 Life cycles and metamorphosis
Every living thing is born or hatches, grows, reproduces and one day dies. This sequence is its life cycle, and new young start the cycle all over again.
Most mammals give birth to live young and feed them milk. Most birds and reptiles lay eggs. But here's a surprise: the platypus is a mammal that lays eggs!
Some animals completely change shape as they grow — this is metamorphosis. A butterfly hatches from its egg as a caterpillar, which eats and eats, then forms a chrysalis. Inside, its body totally changes, and it comes out as a winged butterfly.
Frogs go through metamorphosis too. Out of the egg comes a tadpole that lives in water, with a tail and gills. Over time it grows back legs, then front legs, its tail shrinks and lungs develop. Now it's a frog that can live on land as well!
Key words
- Life cycle
- The stages a living thing goes through, from birth to reproduction.
- Metamorphosis
- An animal completely changing shape as it grows.
- Tadpole
- The young, tailed water stage of a frog.
💡 Did you know? Red-eyed tree frog: It lays its eggs on leaves above water, so the tadpoles drop straight in. The young that drop into the water start life as tadpoles. Meet the animal →
Quick quiz
In a butterfly's life cycle, what comes after the caterpillar?
A) Egg · B) Chrysalis · C) Tadpole · D) Chick
Answer
B) Chrysalis: The caterpillar forms a chrysalis, and the butterfly comes out of it.
How does a tadpole breathe?
A) With lungs · B) With gills · C) With tracheae · D) It doesn't
Answer
B) With gills: A tadpole lives in water and breathes with gills; its lungs develop later.
Which of these is a mammal that lays eggs?
A) Platypus · B) Kangaroo · C) Dolphin · D) Lion
Answer
A) Platypus: The platypus lays eggs but feeds its young on milk, so it's a mammal.
Lesson 12
🐪 Adaptation
Any feature that helps a living thing survive where it lives is called an adaptation. Adaptations are like tools in a toolbox — each habitat needs different tools.
At the poles, the big problem is cold. Polar bears have a thick layer of fat and dense fur. Even the soles of an Arctic fox's feet are furry, and its coat turns white in winter to blend into the snow.
In the desert, the problems are heat and lack of water. Camels store fat in their humps and can drink a huge amount at once. A fennec fox's huge ears give off body heat. Many desert animals hide in the heat of the day and come out at night.
Some adaptations are behaviours, like birds migrating or bears hibernating. Blending in with colours and patterns is called camouflage. Adaptations don't happen overnight: the animals best suited to their surroundings survive more often and pass those features on to their young, over thousands of generations.
Key words
- Adaptation
- A feature that helps a living thing survive in its habitat.
- Camouflage
- Blending into the background with colours and patterns.
- Hibernation
- Spending winter in a long, deep sleep.
💡 Did you know? Fennec fox: The big ears let heat escape and help it hear insects moving under the sand. Meet the animal →
Quick quiz
What does a camel store in its hump?
A) Water · B) Fat · C) Sand · D) Air
Answer
B) Fat: The hump holds fat, not water; the camel uses it when food is scarce.
An Arctic fox turning white in winter is an example of…
A) Migration · B) Camouflage · C) Photosynthesis · D) Respiration
Answer
B) Camouflage: White fur hides the fox in the snow: camouflage.
Which is a behavioural adaptation?
A) A bear hibernating · B) A fennec fox's big ears · C) A polar bear's fat layer · D) A camel's eyelashes
Answer
A) A bear hibernating: Hibernating is a behaviour; the others are body features.
Lesson 13
🧬 Heredity and DNA
Why do we look like our mum or dad? Because inside the nucleus of every cell is a long molecule called DNA. DNA is like an instruction book for how to build our body.
Each "recipe" in this book is called a gene. Genes help decide our eye colour, whether our hair is curly, and lots of other features.
A baby gets half its genes from its mother and half from its father. That's why brothers and sisters look alike but aren't exactly the same — while identical twins share almost the same DNA. Passing features from parents to young is called heredity.
One of the first to discover the rules of heredity was Gregor Mendel. In the 1800s he grew thousands of pea plants and studied how their colours and shapes passed to new plants. But remember: not just genes but also food and surroundings shape how we grow.
Key words
- DNA
- The molecule in the cell nucleus that carries a living thing's instructions.
- Gene
- A section of DNA that helps decide a feature.
- Heredity
- Features passing from parents to their young.
💡 Did you know? Chimpanzee: We share about 98 percent of our DNA with it. Meet the animal →
Quick quiz
Where in the cell is DNA found?
A) In the cell wall · B) In the nucleus · C) In the bone · D) Outside the blood
Answer
B) In the nucleus: DNA is kept in the nucleus, the cell's control centre.
Where does a baby get its genes from?
A) Only its mother · B) Only its father · C) Half from each parent · D) Its brothers and sisters
Answer
C) Half from each parent: Half the genes come from the mother and half from the father.
Which plant did Gregor Mendel use to study heredity?
A) Pea · B) Rose · C) Pine · D) Bamboo
Answer
A) Pea: Mendel studied how the colours and shapes of pea plants were passed on.
Lesson 14
🌍 Ecosystems and protecting nature
Picture a lake: it's home to fish, frogs, plants and tiny creatures. But water, soil, sunlight and temperature matter too. Living things together with their non-living surroundings make up an ecosystem.
The variety of living things in a place is called biodiversity. Tropical rainforests are among the richest ecosystems on Earth. The more biodiversity there is, the better an ecosystem can cope with change.
Today many species are in danger. The biggest threats are habitat loss, pollution such as plastic, climate change and illegal hunting. Scientists track species on the IUCN Red List. Some, like the dodo, are gone forever.
You can help too! Sort your rubbish and use less plastic. Don't waste water or electricity. In nature, don't disturb animals — watch them from a distance. In Türkiye, bald ibises and loggerhead turtles are still here thanks to conservation work.
Key words
- Ecosystem
- The living things in a place together with their non-living surroundings.
- Biodiversity
- The variety of living things in a place.
- Extinction
- When the last member of a species dies.
💡 Did you know? Loggerhead sea turtle: Hatchlings come out at night and head for the glow of the sea — bright beach lights confuse them. Meet the animal →
Quick quiz
Which of these is a non-living part of an ecosystem?
A) Fish · B) Frog · C) Sunlight · D) Moss
Answer
C) Sunlight: Sunlight, water and soil are the non-living parts of an ecosystem.
What is the variety of living things in a place called?
A) Biodiversity · B) Photosynthesis · C) Heredity · D) Respiration
Answer
A) Biodiversity: Biodiversity describes how many different kinds of living things a place has.
How can we help loggerhead turtle hatchlings?
A) Keep the beach dark at night · B) Take hatchlings home · C) Drive on the beach · D) Dig up the eggs
Answer
A) Keep the beach dark at night: Hatchlings head for the glow of the sea; lights on the beach confuse them.